Hyperalgesia induced by low doses of thymulin injections: possible involvement of prostaglandin E2

The immunomodulation of a novel tumor necrosis factor (CgTNF-1) in oyster Crassostrea gigas

Tumor necrosis factor (TNF) is one of the most important cytokines involved in many processes in both vertebrate and invertebrate. In the present study, a new tumor necrosis factor with a typical TNF domain was identified in oyster Crassostrea gigas (designated CgTNF-1). CgTNF-1 shared low sequence identity and similarity with the TNF superfamily members from other vertebrate and invertebrate. After LPS stimulation, the mRNA expression of CgTNF-1 in haemocytes increased significantly and peaked at 12h (1.39±0.12, P<0.05) post treatment, and the expression of CgTNF-1 protein in haemolymph also increased obviously during 6-12h. When the oyster haemocytes were incubated with rCgTNF-1, its apoptosis and phagocytosis rate were both effectively induced and peaked at 12h post the treatment of rCgTNF-1 with the concentration of 100ngmL(-1) (23.3±3%, P<0.01), 50ngmL(-1) (5.3±0.6%, P<0.05) and 10ngmL(-1) (6.7±1.2%, P<0.05), respectively. After the co-stimulation of LPS and rCgTNF-1, the apoptosis and phagocytosis rate of oyster haemocytes, and the activities of PO and lysozyme in the haemolymph all increased significantly, and reached the peak at 12h (apoptosis rate 26.7±1.5%, P<0.01), 12h (phagocytosis rate 8.3±0.6%, P<0.01), 6h (PO 1.11±0.01Umg prot(-1), P<0.01) and 12h (lysozyme 168.9±8.3Umg prot(-1), P<0.05), respectively, which were significantly higher than that in the LPS group. Furthermore, the anti-bacteria activity in the LPS+TNF group was significantly higher than that in the LPS group during 6-12h. All the results collectively indicated that CgTNF-1 was involved in the oyster immunity and played a crucial role in the modulation of immune response including apoptosis and phagocytosis of haemocytes, and regulation of anti-bacterial activity as well as the activation of immune relevant enzymes.

Role of Thymulin or Its Analogue as a New Analgesic Molecule

The thymic peptide thymulin is known for its immunomodulatory role. However, several recent reports have indicated that thymulin is capable of interacting directly and/or indirectly with the nervous system. One of the first lines of evidence of this interaction was obtained in a series of experiments showing the hyperalgesic actions of this peptide. We demonstrated that, at low doses (ng), local (intraplantar) or systemic (intraperitoneal) injections of thymulin resulted in hyperalgesia with an increase in proinflammatory mediators, and that this peptide could act directly on the afferent nerve terminals through prostaglandin-E2 (PGE2)-dependent mechanisms, thus forming a neuroimmune loop involving capsaicin-sensitive primary afferent fibers. In further experiments, systemic injections of relatively high doses (1-25 microg) of thymulin or of an analogue peptide (PAT) deprived of hyperalgesic effect, have been shown to reduce the inflammatory pain and the upregulated levels of cytokines induced by endotoxin (ET) injection. In addition, PAT treatment appeared to alleviate the sickness behavior (motor behavior and fever) induced by systemic inflammation. These effects could be attributed, at least partly, to the downregulation of proinflammatory mediators. Furthermore, when compared with the effects of other anti-inflammatory drugs, PAT exerted equal or even stronger analgesic effects, and at much lower concentrations. Subsequent experiments were designed to examine the effects of intracerebroventricular (i.c.v.) injections of thymulin on cerebral inflammation induced by i.c.v. injection of ET. Pretreatment with thymulin reduced, in a dose-dependent manner, the ET-induced hyperalgesia, and exerted differential effects on the upregulated levels of cytokines in different areas of the brain, suggesting a neuroprotective role for thymulin in the central nervous system (CNS). Preliminary results demonstrate that thymulin inhibits in the hippocampus the ET-induced nuclear activation of NF-kappaB, the transcription factor required for the expression of proinflammatory cytokines genes. Although the mechanism of action of these molecules is not totally elucidated, our results indicate a possible therapeutic use of thymulin or PAT as analgesic and anti-inflammatory drugs.

Cytokines and neuro-immune-endocrine interactions: a role for the hypothalamic-pituitary-adrenal revolving axis

Cytokines, peptide hormones and neurotransmitters, as well as their receptors/ligands, are endogenous to the brain, endocrine and immune systems. These shared ligands and receptors are used as a common chemical language for communication within and between the immune and neuroendocrine systems. Such communication suggests an immunoregulatory role for the brain and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is most commonly associated with the pronounced effects of stress on immunity. The hypothalamic-pituitary-adrenal (HPA) axis is the key player in stress responses; it is well established that both external and internal stressors activate the HPA axis. Cytokines are chemical messengers that stimulate the HPA axis when the body is under stress or experiencing an infection. This review discusses current knowledge of cytokine signaling pathways in neuro-immune-endocrine interactions as viewed through the triplet HPA axis. In addition, we elaborate on HPA/cytokine interactions in oxidative stress within the context of nuclear factor-kappaB transcriptional regulation and the role of oxidative markers and related gaseous transmitters.

Thymulin reduces the hyperalgesia and cytokine upregulation induced by cutaneous leishmaniasis in mice

Cutaneous leishmaniasis (CL) in mice has been shown to produce hyperalgesia and upregulation of interleukin (IL)-1beta and nerve growth factor (NGF) levels. The aim of this study was to investigate the effects of thymulin on CL-induced hyperalgesia and cytokine upregulation. Daily treatment with thymulin (1, 100, and 1000 ng/ip) produced dose-dependent decreases in CL-induced hyperalgesia as assessed by the tail flick and the hot plate tests. The levels of NGF and IL-1beta were determined in the skin tissues of the hind leg in different groups (n = 5 each) of mice over a period of 5 weeks. Mice with CL showed sustained increase in the levels of IL-1beta and NGF which were reversed by thymulin (1 microg). Injection of thymulin only did not alter the nociceptive thresholds or the levels of IL-1beta and NGF. We conclude that thymulin can modulate the hyperalgesia induced by CL by decreasing the levels of the proinflammatory factors IL-1beta and NGF.

Neuroendocrine control of thymus physiology

The thymus gland is a central lymphoid organ in which bone marrow-derived T cell precursors undergo differentiation, eventually leading to migration of positively selected thymocytes to the peripheral lymphoid organs. This differentiation occurs along with cell migration in the context of the thymic microenvironment, formed of epithelial cells, macrophages, dendritic cells, fibroblasts, and extracellular matrix components. Various interactions occurring between microenvironmental cells and differentiating thymocytes are under neuroendocrine control. In this review, we summarize data showing that thymus physiology is pleiotropically influenced by hormones and neuropeptides. These molecules modulate the expression of major histocompatibility complex gene products by microenvironmental cells and the extracellular matrix-mediated interactions, leading to enhanced thymocyte adhesion to thymic epithelial cells. Cytokine production and thymic endocrine function (herein exemplified by thymulin production) are also hormonally controlled, and, interestingly in this latter case, a bidirectional circuitry seems to exist since thymic-derived peptides also modulate hormonal production. In addition to their role in thymic cell proliferation and apoptosis, hormones and neuropeptides also modulate intrathymic T cell differentiation, influencing the generation of the T cell repertoire. Finally, neuroendocrine control of the thymus appears extremely complex, with possible influence of biological circuitry involving the intrathymic production of a variety of hormones and neuropeptides and the expression of their respective receptors by thymic cells.

The regulation of PGE(2) biosynthesis in MG-63 osteosarcoma cells by IL-1 and FGF is cell density-dependent

We investigated the molecular mechanisms by which treatment of the human osteoblast-like cell line MG-63 with interleukin 1beta (IL-1) and/or fibroblast growth factor 1 (FGF-1) elicited prostaglandin biosynthesis. IL-1 induced a 5-fold increase in PGE(2) production compared to controls. While treatment with FGF-1 alone did not affect PGE(2) biosynthesis, it enhanced the formation of PGE(2) by IL-1 by an additional 3- to 5-fold. IL-1-induced PGE(2) biosynthesis accompanied increases in steady-state levels of mRNAs encoding cPLA(2) (10- to 15-fold) and PGHS-2 (>3-fold) and concomitant increases in cPLA(2) protein (>3-fold) and PGHS-2 protein (>1. 5-fold). FGF-1 treatment did not affect PGHS-2 gene expression, but enhanced the effect of IL-1 on PGHS-2 expression by an additional 2- to 3-fold. FGF-1 alone enhanced cPLA(2) expression (5-fold), and the combined effects of FGF-1 and IL-1 on cPLA(2) expression were additive. There was no measurable effect of either agonist on PGHS-1 expression. We also discovered that induction of PGE(2) biosynthesis in response to IL-1 or IL-1/FGF-1 was affected by the density of MG-63 cells in culture. Subconfluent cultures displayed a 3- to 10-fold greater response to IL-1 or IL-1/FGF-1 than confluent cultures. The decreased PGE(2) induction by IL-1 in confluent cultures was associated with reduced IL-1 receptor expression. We conclude that the signaling pathways resulting in PGE(2) biosynthesis in response to proinflammatory agents like IL-1 are subject to complex regulation by additional soluble mediators as well as cell-cell or cell-extracellular matrix interactions.

The role of cytokines and prostaglandin-E(2) in thymulin induced hyperalgesia

We have recently reported that intraperitoneal (i.p.) injection of thymulin at low doses (50 ng) resulted in thermal and mechanical hyperalgesia and upregulation of the level of interleukin-1beta in the liver. In this study, we demonstrate that such injections of thymulin result in a significant elevation in the levels of TNF-alpha (P<0.01), NGF (P<0.01) and PGE(2) (P<0.01) in the liver of the treated rats, in addition to the increase in the levels of IL-1beta. Pretreatment with specific antagonists to each of these factors (polyclonal anti-TNF-alpha, anti-NGF antiserum and IL-1 receptor antagonist) did not result in the abolition of the hyperalgesia as assessed by the paw pressure, hot plate, paw immersion and tail flick tests. However, pretreatment with a combination of the above antagonist and antisera almost completely prevented thymulin-induced hyperalgesia. The cyclooxygenase inhibitor, meloxicam, reversed in a dose dependent manner (0.2, 0.4 and 2 mg/kg) thymulin effects as assessed by the different pain tests. It also abolished the thymulin-induced increase in the level of cytokines and NGF in the liver. Our results indicate that PGE(2) could be the key mediator of the hyperalgesic action of thymulin and the observed upregulation of proinflammatory cytokines and NGF.

Functional interplay between gelatinases and hyperalgesia in endotoxin-induced localized inflammatory pain

The role of ECM-degrading proteinases in normal developmental processes and in pathological conditions is extensively studied. However, few reports describe the role ECM-degrading proteinases play in modulating hyperalgesia. The goal of this study is to describe the regulation of gelatinases during endotoxin mediated local inflammation, induced by intra plantar endotoxin (ET; 1.25 microg/50 microl) injection in Balb/c mice, and to correlate that with hyperalgesia. ET injections induced hyperalgesia, as determined by hot plate and paw pressure tests, which peaked by 24 h and recovered by 48 h post-injection. Contralateral paw of ET injected mice and saline injected paws in control mice elicited no hyperalgesia. Zymography showed that ET and saline injected paws elicited increased gelatinase activity by 9 h after injection. However, only the former maintained high levels of expression of a 90 kD gelatinase up to at least 96 h post ET injection, while in the latter gelatinase expression was down regulated by 24 h. Interestingly, the 90-kD gelatinase was upregulated in the contralateral paw of the ET-injected mice beyond 48 h post injection. Saline injection in that paw, during a time when gelatinases are upregulated, induced hyperalgesia. Intraperitoneal injection of either ZnCl(2) (100 microM), thymulin (5 microg/100 microl), or morphine (2 mg/kg/100 microl) reversed the ET-induced hyperalgesia and suppressed gelatinase activity. Furthermore, intraperitoneal injection of MPI, an ECM-degrading proteinase inhibitor, reversed ET induced hyperalgesia. Taken together, the above suggests that a functional interplay exists between gelatinase upregulation triggered by ET injections and hyperalgesia. The exact mechanism underlying such correlation remains to be determined.

From electrical wiring to plastic neurons: evolving approaches to the study of pain

Clinical and animal experimental evidences accumulated during the past four decades indicate an evolving change, championed by Patrick D. Wall, from the old concept of a specific pain pathway and hard-wired nervous system to a dynamic concept of plastic neural mechanisms underlying nociceptive processing like other sensory neural functions. These include: (1) the reciprocal sharing and interaction of various somatic sensory modalities between the ascending pathways; (2) the activation of spinal gating mechanisms through a dorsal column brainstem spinal loop; (3) the role of plastic changes in the nervous system in the production and maintenance of chronic pain; (4) the evidence showing that processing of nociception involves the activation of a diffuse network of transmitting fiber tracts and brain centers that are not exclusively devoted to pain; and (5) the consideration of chronic pain, at least in part, as a sign or reflection of a dysfunction in neuroimmune-endocrine regulations.

Thymulin induces c-fos expression in the spinal cord of rats which is reversed by meloxicam and morphine

Intraplantar (i.pl.) injections of thymulin have been shown to produce hyperalgesia in rats through a prostaglandin E2-dependent mechanism. This study aimed at investigating if such injections can produce sustained activation of spinal neurons by mapping the fos-like-immunoreactivity (FLI) as a marker for this activation. Our results showed that thymulin produces significant and sustained FLI in neurons located in spinal laminae known to be involved in nociception. Pretreatment with either morphine or meloxicam (a cyclooxygenase inhibitor) revealed differential effects on FLI and the hyperalgesia induced by thymulin. These findings support the hypothesis that thymulin can affect central neurons either directly or through the peripheral nerve terminals.

Involvement of capsaicin sensitive primary afferents in thymulin-induced hyperalgesia

Intraplantar (5 ng) or intraperitoneal (50 ng) injections of thymulin, produced both thermal and mechanical hyperalgesia in rats. In this report, we show that ablation of capsaicin sensitive primary afferents (CSPA) can alter or abolish thymulin-induced hyperalgesia. Different groups of rats were subjected to either treatment with capsaicin or to surgical subdiaphragmatic vagotomy (SDV). Both capsaicin and SDV reduced significantly thymulin-induced hyperalgesia. On the other hand, these treatments elicited differential effects on the modulation by thymulin of the levels of nerve growth factor and interleukin 1beta. We conclude that the hyperalgesic effects of i.p. thymulin are mainly mediated through the CSPA fibers.